Tris-(hydroxyamino)triazines: high-affinity chelating tridentate O,N,O-hydroxylamine ligand for the cis-VVO2+ cation

Abstract

The treatment of the trichloro-1,3,5-triazine with N-methylhydroxylamine hydrochloride results in the replacement of the three chlorine atoms of the triazine ring with the function –N(OH)CH₃ yielding the symmetrical tris-(hydroxyamino)triazine ligand H₃trihyat. Reaction of the ligand H₃trihyat with NaV^VO₃ in aqueous solution followed by addition of Ph₄PCl gave the mononuclear vanadium(V) compound Ph₄P[V^VO₂(Htrihyat)] (1). The structure of compound 1 was determined by X-ray crystallography and indicates that this compound has a distorted square-pyramidal arrangement around vanadium. The ligand Htrihyat²⁻ is bonded to vanadium atom in a tridentate fashion at the triazine ring nitrogen atom and the two deprotonated hydroxylamido oxygen atoms. The high electron density of the triazine ring nitrogen atoms, which results from the resonative contribution of electrons of exocyclic nitrogen atoms, leads to a very strong V–N bond. The cis-[V^VO₂(Htrihyat)]⁻ species exhibits high hydrolytic stability in aqueous solution over a wide pH range, 2.5–11.5, as was evidenced by potentiometry.